Digital signal processed touchscreen system

ABSTRACT

Digital signal processed touchscreen system. The invention employs amplitude ramped signals across a touchscreen. The pattern to which the amplitude ramped electric signals are provided may be located on the surface of the touchscreen, or alternatively on the backside of the touchscreen. The signal processing employed by the invention, using digital signal processing techniques, is operable to discern a user&#39;s touch and to determine its location. A dielectric, protective surface is used to enable implementation into a wide variety of applications, including those applications that are environmentally rugged and have, until now, been too rugged for prior art touchscreen systems. The invention employs a user generated unbalanced capacitive load generated on the touchscreen to identify the location of the user&#39;s touch.

CROSS REFERENCE TO RELATED PATENTS/PATENT APPLICATIONS ContinuationPriority Claim, 35 U.S.C. §120

The present U.S. Utility patent application claims priority pursuant to35 U.S.C. §120, as a continuation, to the following U.S. Utility patentapplication which is hereby incorporated herein by reference in itsentirety and made part of the present U.S. Utility patent applicationfor all purposes:

1. U.S. Utility application Ser. No. 11/211,272, entitled “Digitalsignal processed touchscreen system,” filed Aug. 25, 2005, pending,which claims priority pursuant to 35 U.S.C. §119(e) to the followingU.S. Provisional Patent Application which is hereby incorporated hereinby reference in its entirety and made part of the present U.S. Utilitypatent application for all purposes:

-   -   a. U.S. Provisional Application Ser. No. 60/604,655, entitled        “Digital signal processed touchscreen system,” filed Aug. 26,        2004.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The invention relates generally to man to machine interfaces (MMIs)implemented using touchscreens; and, more particularly, it relates to acapacitively coupled system.

2. Description of Related Art

The use of MMI systems has been ongoing for some time now. A variety ofeveryday activities employ some form of MMI. For example, banking maynow be performed without the assistance of bank personnel by using anautomatic teller machine (ATM); a driver may purchase gasoline withoutinteracting with a sales agent using the interfaces commonly located atthe gas pumps. However, these two examples illustrate how thedevelopment of rugged MMIs has often taken the route of employingrugged, plastic-type keys located near a display. This has been theindustries solution to try to provide a rugged, durable, MMI that iscapable of withstanding a variety of environmental and use-inducedstresses. Some MMIs do in fact employ a system where a user may makeselections by actually touching and interacting with the display itself(in a true touchscreen system), but such applications are not verywidespread, and they are nearly never placed in environments where themay the touchscreen is exposed to a rugged environment. These prior arttouchscreen systems often find themselves within very environmentallyprotected installations.

These prior art touchscreen systems typically employ a pattern on acoating that is placed on the surface of the touchscreen that a userdoes in fact touch. This approach often includes the use of some type ofclear coatings over the surface-laid pattern. These patterns aretypically very delicate in nature and the engineering required to ensureproper protection of the pattern can be quite extensive, and sometimesvery expensive, in some instances. Clearly, the fact that the pattern isplaced on the touchscreen surface and is exposed to the environmentsignificantly limits the applications in which many prior arttouchscreens may be used. For example, the environmental considerationsof humidity, extreme heat and cold (including large and/or rapidtemperature changes), and other environmental considerations limit theimplementation of such prior art touchscreen technologies.

Many such prior art technologies employ a continuous pattern on thesurface of a touchscreen. Oftentimes, the corners of the touchscreen aresimultaneously energized with a common signal, and the entiretouchscreen surface is energized. When a user touches the surfacematerial, the user's touch interacts with the signals that are providedby the pattern on the surface of a touchscreen. This prior art approachsuffers from the fact that the coating is again resident on the surfaceof the touchscreen where it is exposed to a variety of potentiallyharmful effects. The degradation of this coating material will degradethe overall performance of the touchscreen system, if not result in thecessation of functionality entirely.

Another prior art employs a matrix type of pattern on the backside of atouchscreen having rows and columns located on the backside of thetouchscreen surface that is commonly made up of some protectivematerial. This may be viewed as being a digitally arranged pattern,having discrete rows and columns that may be used as possible touchlocations. The system's ability to discern the location of a user'stouch is governed by the pre-arranged layout of the matrix type pattern.Employing a row and column design allows the capitalization ofinformation retrieved from the row and column associated with a user'stouch. The row and column pattern (on the backside of the surface of thetouchscreen) are energized and the associated fields communicativelycouple through the protective surface material. The row and columnapproach typically includes at least one additional layer that separatesthe rows and columns of the row and column matrix. This additional layercan complicate the touchscreen system, in that, there is yet anotherlayer of material through which signals' communicatively coupling mustoccur for proper operation and the ability to detect a user's touch.

However, one of the several deficiencies of this approach is inherent tothe row and column implementation in terms of resolution and thesystem's ability to discern the true location of the user's touch. Theprocessing and manufacturing of the system, based on the proximity ofthe rows and columns, largely governs the resolution of the touchscreensurface. In addition, there is often a limit to the closeness of theproximity of the rows and columns that may be used while still allowingfor the signal processing to extract precisely which row and whichcolumn is associated with a user's touch. This density into which therows and columns may be placed also prohibits its implementation intoapplications of relatively small real estate. Applications that requirea relatively small implementation or are extremely real estate/spaceconscious may not be candidates for this technology. Particularly whenthese applications require a relatively large number of selectableoptions on the touchscreen, this particular technology simply cannotmeet these needs. The ability of this row and column implementation may,on one hand, enable application in more rugged environments (given thatthe rows and columns are located on backside layers of the touchscreen);however, on the other hand, this prior art approach fails to meet theneeds of other applications (including those requiring higher resolutionof selectable options on the touchscreen and/or real estate/spaceconscious designs).

Moreover, as the closeness of the rows and columns increases, there isever more cross coupling between them. This may require additionalinsulating material between them. This may compete with thecommunicative coupling of the desired signal through the surface'sprotective material. In addition, the cross coupling between extremelyclose rows and columns may be so great that the signal processing,absent more advanced and sometimes very complex methods, may simply beunable to discern the true location of a user's touch and to determineits location.

Other prior art technologies are operable to use a pen-like pointer thatis used to select portions of a touchscreen. In such implementations,the pen actually interacts with the touchscreen system, in that, thecurrent that travels from the surface of the touchscreen through thepen-like pointer is measured in the calculations that are performed todetermine the user's touch location, when the pen-like pointer touchesthe touchscreen.

Further limitations and disadvantages of conventional and traditionalsystems will become apparent to one of skill in the art throughcomparison of such systems with the invention as set forth in theremainder of the present application with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to apparatus and methods of operationthat are further described in the following Brief Description of theSeveral Views of the Drawings, the Detailed Description of theInvention, and the claims. Other features and advantages of the presentinvention will become apparent from the following detailed descriptionof the invention made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a system diagram illustrating an embodiment of basic operationof a touchscreen system that is built in accordance with certain aspectsof the invention.

FIG. 2 is a system diagram illustrating an embodiment of a touchscreensystem that is built in accordance with certain aspects of theinvention.

FIG. 3 is a system diagram illustrating another embodiment oftouchscreen system that is built in accordance with certain aspects ofthe invention.

FIG. 4 is a system diagram illustrating another embodiment of atouchscreen system that is built in accordance with certain aspects ofthe invention.

FIG. 5 is a functional block diagram illustrating an embodiment of atouchscreen processing method that is performed in accordance withcertain aspects of the invention.

FIG. 6 is a functional block diagram illustrating another embodiment ofa touchscreen processing method that is performed in accordance withcertain aspects of the invention.

FIG. 7 is a functional block diagram illustrating another embodiment ofa touchscreen processing method that is performed in accordance withcertain aspects of the invention.

FIG. 8 is a functional block diagram illustrating another embodiment ofa touchscreen processing method that is performed in accordance withcertain aspects of the invention.

FIG. 9 is a diagram illustrating an embodiment of a linear resistivepattern that is arranged around the perimeter of a touchscreen that isbuilt in accordance with certain aspects of the invention.

FIG. 10 is a circuitry diagram illustrating an embodiment of a cornerdrive circuitry that is built in accordance with certain aspects of theinvention.

FIG. 11 is a circuitry diagram illustrating an embodiment of a cornermeasurement circuitry that is built in accordance with certain aspectsof the invention.

FIG. 12 is a circuitry diagram illustrating an embodiment of a high passsingle pole filter/adder circuitry that is built in accordance withcertain aspects of the invention.

FIG. 13 is a circuitry diagram illustrating an embodiment of a low passdouble pole filter/gain stage circuitry that is built in accordance withcertain aspects of the invention.

FIG. 14 is a circuitry diagram illustrating an embodiment of a nullsignal generation circuitry that is built in accordance with certainaspects of the invention.

FIG. 15 is a circuitry diagram illustrating an embodiment of a nullsignal adding circuitry that is built in accordance with certain aspectsof the invention.

FIG. 16 is a circuitry diagram illustrating an embodiment of a digitalsignal processing (DSP) circuitry that is built in accordance withcertain aspects of the invention.

FIG. 17 is a functional block diagram illustrating an embodiment offunctional cooperation performed by the various circuitries shown withinthe FIGS. 9, 10, 11, 12, 13, 14, 15, and 16.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a solution that maintains a high degree ofresolution across a touchscreen surface while also offering an extremelyrobust and rugged package making it amenable to implementation into avariety of applications. One particularly desirable application includesthose touchscreen applications that are located outdoors. Whereas manyprior art technologies may typically not be implemented outdoors,largely due to the fluctuations of environment including temperature andhumidity fluctuations, the invention may be implemented outdoors veryeasily. The continuous nature of the amplitude ramped field used by theinvention also ensures a high degree of resolution compared to the rowand column based prior art touchscreen systems that have attempted tobridge the gap and offer outdoor application.

A resistive linearized pattern may be placed on the backside of aprotective dielectric surface. The protective dielectric surface may becomposed of a tempered glass surface in some instances. However, theprotective dielectric surface may also be composed of other types ofdielectric materials as well without departing from the scope and spiritof the invention.

An amplitude ramped field is generated by energizing the pattern on thebackside of the touchscreen. In one embodiment, the touchscreen includesa substantially rectangular shape, and the corners of the touchscreenare operable as nodes that are communicatively coupled to drive signalcircuits. The drive signal circuits, provided to each of the corners ofthe touchscreen, are comparable in terms of components, yet and they aredriven differently at various points in time. By analyzing measurementstaken from the corners at various points in time, the particularlocation of a user's touch may be discerned. In addition, aspects of theinvention is also operable within an energy savings mode when no usertouch is detected on the touchscreen surface, and the touchscreen systementers into a touch detection mode when it is determined that a user hasin fact touched the touchscreen.

It is also noted that the certain aspects of the invention employ signalprocessing that is operable within systems that choose to include apattern on the surface of the touchscreen as well. In this case, theamplitude ramped field will be generated by the pattern located on thefront side of the touchscreen surface rather than being generated by apattern on the back side of the touchscreen and communicatively coupledthrough the touchscreen surface. Therefore, certain aspects of theinvention are operable within implementations that desire to use a frontside pattern, such as one that is covered with some type of transparentprotective coating.

FIG. 1 is a system diagram illustrating an embodiment of basic operationof a touchscreen system 100 that is built in accordance with certainaspects of the invention. A touchscreen 105 includes four corners thatare each provided with excitation signals. At one instant, the two lefthand corners (upper left UL and lower left LL) are both provided with afull scale AC signal. In addition, at the same instant, the two righthand corners (upper right UR and lower right LR) are both provided witha virtual ground signal. The result is an amplitude ramped field(amplitude ramped AC signal) across the touchscreen 105. Current isinjected into each of these four corners of the touchscreen 105. Inaddition, current is also exiting the touchscreen 105 at each of thecorners of the touchscreen 105 as well. When a user touches thetouchscreen 105, then the amount of current that does exit the cornersof the touchscreen 105 will be altered.

By employing an amplitude ramped AC signal across the surface of thetouchscreen 105, when a user touches the touchscreen 105 in a particularlocation, the interaction of the user and the AC signal then effectuatesan unbalanced capacitive load on the touchscreen. As the voltage rampedAC waveform crosses the touchscreen 105, having a maximum voltageamplitude at one side and a minimum voltage amplitude (or zero) at theother side, a user's touch at any point on the touchscreen will return avarying amplitude current flow based on the position of the user'stouch.

By knowing the current that is injected into the corners of thetouchscreen 105, and also by monitoring the current that exits thecorners, the invention is operable to provide inputs from all of thecorners into a processing circuitry that is operable to identify thelocation of the user's touch on the screen. All of the corners' outputsare simultaneously provided to this processing circuitry; the inventionneed not individually measure the four corners as they are all handledsimultaneously using the single circuit. Those having skill in the artwill recognize that any number of samples/measurements may be takenwithin a given cycle to provide for a higher degree of confidence for aparticular measurement. Based upon the now changed current that doesexit the four corners of the touchscreen 105, the location of the user'stouch on the touchscreen 105 may then be accurately discerned.

In addition, as will also be described in other of the variousembodiments, the direction of the amplitude ramped field is reversed sothat the ramping of the amplitude ramped field goes from right to left;the direction of the ramping of the amplitude ramped field may also bealtered to extend from top to bottom and vice versa from bottom to topacross the touchscreen 105. During each of these instances, the currentthat is injected into the four corners will be different, and themeasurements of the currents exiting the currents will also bedifferent.

The currents that exit the four corners of the touchscreen 105 are alladded simultaneously into the total current summing circuitry 110. Whenthe directions of the amplitude ramped field across the touchscreen 105are changed, the total current flow exiting all of the four corners maybe viewed as being one current measurement. For example, at one instance(time 1), when the UL and LL corners are at full signal and the UR andLR corners are at virtual ground, the total current measurementconstitutes a sample X. Then, (time 2) when the direction of theamplitude ramped field is reversed (the UR and LR corners are at fullsignal and the UL and LL corners are at virtual ground), then the totalcurrent measurement constitutes a sample INVX.

Similarly, (time 3) when the direction of the amplitude ramped fieldextends from the top to the bottom (the UL and UR corners are at fullsignal and the LL and LR corners are at virtual ground), the totalcurrent measurement constitutes a sample Y. Then, (time 4) when thedirection of the amplitude ramped field extends from the bottom to thetop (the LL and LR corners are at full signal and the UL and UR cornersare at virtual ground), the total current measurement constitutes asample INVY.

Driving the touchscreen 105 in this way (using the amplitude ramped ACfield) causes an unbalanced communicatively coupled load across thetouchscreen 105. Any capacitance added or removed (as with a user'stouch) will be linearly coupled from full scale to zero, and inject acharge, depending on the position of touch on the screen. The totalcurrent flow I (from all the corners) may then be viewed as having aresistive component and an unbalanced capacitive component: totalcurrent flow I=I_(XRES)+I_(XC(unbalanced)). Then, after the measurementsX, INVX, Y, and INVY are generated using the total current summingcircuitry 110, they are then provided to a resistance based currentsubtraction circuitry 120. The resistive component of the total currentis then subtracted away, leaving only the unbalanced capacitivecomponent: I−I_(XRES)=I_(XC(unbalanced)); when the currents based on theresistance of the screen I_(XRES) are removed only the unbalancedcurrent portions remain.

Touching the screen adds to the signal based on the location of thetouch. This alone is not enough to determine touch location, but whencompared to total impedance or coupled with an inverted axis reading avery accurate location of touch can be found. In doing this, a touchlocation determination circuitry 130 employs multiple readings (such asthose associated with the four amplitude ramped field directionsassociated with X, INVX, Y, and INVY). It is also noted here that,although this embodiment is depicted with respect to 2 directions (e.g.,X and Y), this technology could easily be adapted and applied withrespect to only a single axis (e.g., only X or only Y) with even reducedcomplexity. For example, an analogous implementation could be applied toa single axis device that could employ some uni-directional userinterface (e.g., slide bars) whose location/position is selected by auser.

FIG. 2 is a system diagram illustrating an embodiment of a touchscreensystem 200 that is built in accordance with certain aspects of theinvention. The FIG. 2 may be viewed as being a snapshot of a touchscreensystem at time 1 as described with respect to the FIG. 1. However, othertime instances clearly may also occur in which the other of the timesshown in the FIG. 1 may also occur.

Corners of a touchscreen 205 are provided with signals from drive signalcircuits. The UL corner has a drive signal circuit 210; the UR cornerhas a drive signal circuit 220; the LL corner has a drive signal circuit230; and the LR corner has a drive signal circuit 240. The drive signalcircuits 210, 220, 230, and 240 also operate as current sensors at thecorners of the touchscreen 205. Even though current is effectivelyinjected into each of the four corners of the touchscreen 205 by thedrive signal circuits 210, 220, 230, and 240, there is also current thatexits from each of the four corners as well. A digital wave generatorchip, having a built in DAC, is operable to supply a wave functionhaving a particular amplitude to the corner driver circuits by way of adigitally controlled amplitude circuit. In one embodiment, a digitalsine wave generator chip with a built in DAC may be employed to supply aprocessor programmable spectrally pure sine wave of fixed amplitude tothe corner driver circuits by way of a digitally controlled amplitudecircuit. Each of the drive signal circuits 210, 220, 230, and 240 may beimplemented such that they can deliver a low impedance zero signal tofull scale amplitude with 8 bits of resolution to the corner drivecircuits. It is also noted here that the frequency of the signalsprovided by the various digital wave generator chips may be different.There may be some embodiments where the signals generated in the X and Ydirections are the same (e.g., having a similar signal shape, amplitude,phase, and frequency); however, multiple signals that are different mayalso be employed (e.g., having different signal shapes, amplitudes,phases, and/or frequencies). For one example of an alternativeembodiment, a DSP (Digital Signal Processor) may be employed to generateeach of the different signals that are provided to corresponding DACs.In one instance, a first frequency may be employed to drive the signalsfrom side to side across the touchscreen, and a second frequency may beemployed to drive the signals from top to bottom across the touchscreen.Other of the parameters (e.g., signal shape, amplitude, and/or phase)may also be varied for each of the differently directed signals.

Each corner of the touchscreen glass employs a comparable “DRIVER”circuit (drive signal circuits 210, 220, 230, and 240) where an appliedinput “drive” signal of AC potential or “ground” will drive the attachedcorner to the same signal level as the input signal. Each of the drivesignal circuits 210, 220, 230, and 240 has two outputs. One of theoutputs (output #1) is attached to the sensor glass of the touchscreen205 and the second output (output #2) is attached to a subtractioncircuit. Each of the four corners has an associated subtraction circuitshown as subtraction circuits 212, 222, 232, and 242.

As an example, the output #2 from the UL corner is representation of thecurrent entering and exiting output #1 plus the input “drive” signalprovided by the drive signal circuit 210. The output #2 is attached to acircuit where the input “drive” signal is removed from output #1,namely, the subtraction circuit 212. The output of the subtractioncircuit 212 is shown as the reference numeral A, and its destination isshown in FIG. 3. The signal provided to the subtraction circuit 212 isrepresentative of the current entering and exiting the UL corner of thetouchscreen 205. This situation may be referred to as being the sample X(or the X-axis). When an axis is energized the lower left LL corner andupper left UL corner “DRIVER” circuits (drive signal circuits 210 and230) are driven with an AC voltage of the same polarity on theirrespective input “drive” signals, both corners being referred to as HIGHSIDE. The ground side of the touchscreen 205, the upper right UR andlower right LR “DRIVER” circuits (drive signal circuits 220 and 240) aredriven to “ground”, both corners being referred to as LOW SIDE.

On the HIGH SIDE, the AC signal out of the “DRIVER” circuit output#2will represent the total current flowing in and out of that corner plusthe voltage of the applied input “drive” signal. When the input drivesignal is stripped off or subtracted from output#2, using thesubtraction circuitry, then the remaining signal will be a voltagerepresentation of only the current flowing through the corner of thescreen attached to output#1.

On the LOW SIDE, the AC signal out of the “DRIVER” circuit output#2 willrepresent the total current flowing in and out of that corner plus thevoltage of the applied input “drive” signal (which is zero). When theinput drive signal is stripped off or subtracted from output#2 then theremaining signal will be a voltage representation of only the currentflowing through the corner of the screen attached to output#1. Since thecircuit is operating with a DC or ground input the circuit becomes avirtual ground on its output#1. Output#2 will therefore contain an ACvoltage representation of only the current flowing through the corner ofthe screen attached to output#1 but opposite in phase of the signalsdriving the HIGH SIDE circuits.

The outputs of the four subtraction circuits 212, 222, 232, and 242(shown as reference numerals A, B, C, and D) are all provided to a highpass single pole filter/adder circuitry 310 as shown and described belowin FIG. 3.

FIG. 3 is a system diagram illustrating another embodiment oftouchscreen system 300 that is built in accordance with certain aspectsof the invention. Again, the outputs of the four subtraction circuits212, 222, 232, and 242 in the FIG. 2 (shown as reference numerals A, B,C, and D in the FIG. 2) are all provided to the high pass single polefilter/adder circuitry 310. Again, all of the outputs from all of thefour corners of a touchscreen are treated similarly, in that, they eachpass through a respective subtraction circuit, and they are all thenpassed simultaneously to the high pass single pole filter/addercircuitry 310 where the individual corner signals are passed through ahigh pass single pole filter and added together. The high pass filteringoccurs due to AC coupling between the stages with a lower cutofffrequency around some selected frequency. This frequency may be in therange of 15 kHz (kilo-Hertz) in some embodiments. Adding the outputs ofthe HIGH SIDE and LOW SIDE driver circuits effectively removes thecurrent portion of the signal due solely to the resistance across thetouchscreen, leaving only the unbalanced reactive portion of the currentas a voltage signal. Again, it is this unbalanced reactive portion thatis most greatly indicative of a user's touch.

The output of the high pass single pole filter/adder circuitry 310 isfed to a low pass double pole filter/gain stage circuitry 320. At thispoint a single signal, output from the low pass double pole filter/gainstage circuitry 320, containing only the unbalanced reactive current, isamplified by some factor and is fed into a double pole low pass filter;the amplification factor may be 10 in certain embodiments. The low passfilter at this stage includes an upper cutoff frequency that isappropriately selected to reduce high frequency interference/noise. Forexample, this upper cutoff frequency may be in the 80 kHz range or evenhigher in the 500 kHz range (or even higher) in alternative embodiments.

The output of the low pass double pole filter/gain stage circuitry 320is provided to a nulling/adding circuitry 330. In addition, a nullingsignal generation circuitry 335 provides a null signal to thenulling/adding circuitry 330. A digital sine wave generator chip with abuilt in DAC will supply a processor programmable spectrally pure sinewave of varying amplitude and phase to the nulling/adding circuit 330.The unbalanced reactive load on the touchscreen will take the form of asine wave with a phase shift from the primary touchscreen drive signal.The amplitude and phase of the signal will be the integration of all theunbalanced capacitive reactance in the circuit. This includes thebackground grounding capacitive reactance of the screen and any usertouch reactance. Measuring this signal without a touch and removing it(nulling) leaves only the current associated with the user's touch; itis then left in the form of amplitude changes to the signal.

By generating a sine wave −180 degree phase with and of similaramplitude and adding the touchscreen signal can be almost completelyzeroed. The remaining signal will contain some unbalanced capacitivereactance. Any changes to this signal will be due to a number ofparameters including noise induced into the touchscreen or circuit,temperature variations to the circuits or touchscreen, humidityvariations to the circuit or touchscreen, and a user's touch of thetouchscreen. The change associated with a user's touch is of highdesirability in discerning the location of a user's touch. This signalportion, associated with the unbalanced capacitive reactance, is thenprovided to a final low pass filtering circuitry 340. The low passfiltering circuitry 340 includes an upper cutoff frequency that isappropriately selected to reduce high frequency interference/noise. Forexample, this upper cutoff frequency may be in the 80 kHz range or evenhigher in the 500 kHz range (or even higher) in alternative embodiments.At this point, the waveform should be very pure spectrally. The finaloutput will also be scaled appropriately for the analog input stage tofollow.

A gain/analog to digital converter (ADC) circuitry 350 operates on theremaining signal to clamp it to ground and to send it through aprocessor-controlled variable gain amplifier having a dynamic range ofapproximately 0-36 dB. The processor is operable to test the signal andto amplify it to some range near full scale of the awaiting 20MSPS 12BITADC. Now that the signal is in digital format, the invention is operableto employ DSP techniques (using DSP circuitry 360) to discriminate auser's touch and its location on a touchscreen.

FIG. 4 is a system diagram illustrating another embodiment of atouchscreen system 400 that is built in accordance with certain aspectsof the invention. The touchscreen system 400 shows a touchscreen surface405 that a user is able to contact to select any number of options. Alinearized resistive pattern 407 is on the backside of the touchscreensurface 405. It is noted that the linearized resistive pattern 407, aswell as any other resistive pattern and/or linear resistive patterndescribed herein, may be viewed as being situated on top of a conductivecoating. As one example, the linearized resistive pattern 407 may beimaged or printed onto a conductive Indium Tin Oxide (ITO) coating. Forexample, the linearized resistive pattern 407 may be some type of metalink of low resistance printed on any higher sheet resistance conductor.The resistance typically referred to in terms of a certain resistanceper unit area (e.g., Ω/). It is the particular patterning (spaces andconductors as shown in FIG. 9) of the resistive pattern 407 on the sheetconductor that linearizes the impedance across the touchscreen.

As the linearized resistive pattern 407 is energized on the backside ofthe touchscreen surface 405 using circuitry connected to the linearizedresistive pattern 407, an amplitude ramped field, shown as an amplituderamped AC signal, is then communicatively coupled through thetouchscreen surface 405 so that a user's touch will in fact affect theamplitude ramped field thereby enabling the touchscreen system 400 todetect the location of a user's touch. Again, it is also noted that theinvention is still operable within touchscreen systems that desire toemploy a resistive pattern on the surface of the touchscreen surface405. However, it is understood that by employing the linearizedresistive pattern 407 on the backside of the touchscreen surface 405,then the touchscreen system 400 is operable within many differentapplications including those within rugged and stressful environments.

It is noted here that the user's touch to the touchscreen is actually onthe opposite side of the touchscreen on which where the linearizedresistive pattern 407 is implemented. In effect, it is the modificationof the field amplitude ramped field by the user's presence that isdetected; the amplitude ramped field actually projects out of the frontof the touchscreen surface 405 (i.e., the amplitude ramped fieldprojects through the touchscreen surface 405). The linearized resistivepattern 407 is not actually physically touched by the user (as thetouchscreen surface 405 is interposed between the user interface and thelinearized resistive pattern 407). This capability of not requiring anactual physical touch to the linearized resistive pattern 407 allows amuch broader range of application areas when compared to prior artapproaches and designs.

This capability may be viewed as being that of a 3-D (three-dimensional)capable sensing device. As one example, a user's presence may bedetected a particular distance away from the touchscreen surface 405itself. This capability is very desirable in the medical industry, wheremany medical professionals have their hands enclosed in protectiveplastic gloves at times, and it is burdensome to remove gloves tointeract with such a touchscreen system 400, then subsequently put onadditional gloves to continue with the medical services or tasks athand. Some other desirable application areas would be where a user'shands (and/or gloves) are often soiled or dirty. For example, in the oilindustry, the hands of various users may be oily, and it would be verydesirable to employ such a 3-D capable device to allow user interactionwithout actually requiring the user physically to touch the touchscreen,but merely to interact closely with it. Clearly, there are a widevariety of application areas where this 3-D sensing capability would bedesirable. Certain aspects of the invention have demonstrated this 3-Dcapability to detect a user's hand at approximately 6 inches from thesurface of a touchscreen surface.

As also described in other sections, the direction of an amplituderamped field may be switched during operation of the touchscreen system400. For example, at a time 1, a sample X may be taken. At a time 2, areversed amplitude ramped field may provide for a sample INVX to betaken. The amplitude ramping of the amplitude ramped field is shown attimes 1 and 2 in the FIG. 4.

Similarly, the direction of the amplitude ramped field may be changedyet again (vertically: top to bottom) for a sample Y to be taken at atime 3 and for a sample INVY at a time 4 to be taken when the field ischanged yet again (vertically: bottom to top). A number of samples maybe taken for each of the sample X, INVX, Y, and INVY to provide greatercertainty of the measurement. The touchscreen system 400 may cyclecontinuously through the above-described embodiment by taking andmonitoring the four samples first to detect the existence of a user'stouch and second to discriminate the location of a user's touch.

For example, the system may operate in one mode (a power savings mode)when no user touch is detected for a period of time. Samples would betaken less often with periods of minimal power draw between samples (Zaxis combined with periods of no drive to the corners of thetouchscreen). Then, after the touchscreen system 400 does detect auser's touch, then the system could enter into the sampling of the X,INVX, Y, and INVY measurements and then cycle continuously for a periodof time during which there is in fact user interaction. Then, after aperiod of time when there is no detected user interaction, thetouchscreen system 400 could enter into a power savings mode again.

FIG. 5 is a functional block diagram illustrating an embodiment of atouchscreen processing method 500 that is performed in accordance withcertain aspects of the invention. From certain perspectives, thetouchscreen processing method 500 may be viewed as being digitalprocessing and digitally controlled processing. In block 505, the driveand Direct Digital Synthesis (DDS) are initialized. Then, in block 510,the drive and null digital to analog convert (DAC) are initialized. Inblock 515, the drive and null signal amplitude are zeroed. In block 520,a variable gain amplifier (VGA) is set to zero. In block 525, the zerosignal from the touchscreen is spectrum analyzed. In block 530, thedrive frequency having the lowest noise, within a particular frequencyrange is selected. For example, this frequency range may be between 50kHz and 150 kHz in one embodiment. Then, in a block 535, the drive andnull signal frequency are set.

In block 540, the signals X, INVX, Y, INVY, Z are nulled. In performingthe nulling of the signals, the phase and amplitude of the drive signalis tested. The null phase and amplitude are adjusted to cancel the drivesignal at the ADC. Then, the null offset phase and amplitude data arestored for each signal. The VGA is then adjusted so that the signal isapproximately half ADC scale.

Then, the signals X, INVX, Y, INVY, Z are then sampled in block 545. Thedrive signals are set, and the null phase offset and amplitude are alsoset. The ADC is read where readings for one or more full cycles of drivefrequency constitute a block. The data will be handled in blocks basedon frequency and the ADC speed. The data are read in from the ADC to DSPrandom access memory (RAM). Processing is performed on the data block tofind the amp, phase, and magnitude (APM) of the data. Then the valuescorresponding to A, P, M are stored. Then, in block 550, blockintegration is performed based on the signal strength. The VGA isadjusted in block 555 to keep the signal inside of the ADC's full scale.The DSP is operable to perform any other desired filtering of the data.

Now, the monitoring of the Z axis may be viewed as being an alternativeembodiment in certain situations. The Z is made by driving the fourcorners of the touchscreen with the same amplitude signal. No current isdriven across the screen and no orthogonal touch position information isavailable. The Z need not always be monitored for proper systemperformance. However, Z may be monitored, as shown in an alternativeblock 560 for identifying Nulling adjustments. The Z may be monitoredfor relatively slowly changing parameters such as those associated withslowly changing environmental conditions including temperature andhumidity conditions that may affect the operating points of the variouscircuitry employed within the system. In addition, Z may be used tooperate a touchscreen system within an energy conservation mode and thenwhen a change is determined, then the touchscreen system may enter intouser touch location identification sequence.

Whether or not Z is monitored, the touchscreen processing method 500continues to calculate X, Y data values as shown in a block 565. Indoing so, the X position and Y positions are calculated as follows:

${Xpos} = \frac{X}{\left( {X + {INVX}} \right)}$${Ypos} = \frac{Y}{\left( {Y + {INVY}} \right)}$

These equations do not include touch null offsets. It is also noted thatvalues of X and INVX generally represent a touchscreen's unbalancedcapacitive load X_(UNBAL) (including any user touch induced unbalancedcapacitive load X_(TOUCH)) but are equivalent in amplitude.

If we instead desire to include the effects of the nulling (and alsoseparating the touchscreen's unbalanced capacitive load portion with theunbalanced capacitive load portion associated with a user's touch), thenthe following equations could be used.

${Xpos} = \frac{\left( {X_{UNBAL} + X_{TOUCH} - X_{NULL}} \right)}{\begin{matrix}{\left( {X_{UNBAL} + X_{TOUCH} - X_{NULL}} \right) +} \\\left( {{INVX}_{UNBAL} + {INVX}_{TOUCH} - {INVX}_{NULL}} \right)\end{matrix}}$${Ypos} = \frac{\left( {Y_{UNBAL} + Y_{TOUCH} - Y_{NULL}} \right)}{\begin{matrix}{\left( {Y_{UNBAL} + Y_{TOUCH} - Y_{NULL}} \right) +} \\\left( {{INVY}_{UNBAL} + {INVY}_{TOUCH} - {INVY}_{NULL}} \right)\end{matrix}}$

Then, in a block 570 the data is formatted and output in a block 575.

Regarding the block data acquisition and processing, it is noted thatthe drive signal will be set at a known phase angle and data will beacquired into the DSP memory. The data acquired will be some number ofsamples of data per cycle of the drive signal based on the ADC speed,cycle length, and the available RAM. Data acquisition and storagetypically be the slowest operation by the processor by a relativelylarge margin. Once in memory, spectral analysis/frequency analysiscalculations will be performed on the block of data resulting in amp,phase, and magnitude (APM) readings for that block of data. Severalblocks will be processed if necessary in this manner and the APMreadings integrated into total APM readings. Block readings will beperformed on all necessary signals (X, INVX, Y, INVY, Z) until a totaldata set has been acquired. The number of blocks integrated may vary butwill remain consistent across a set of signal readings.

FIG. 6 is a functional block diagram illustrating another embodiment ofa touchscreen processing method 600 that is performed in accordance withcertain aspects of the invention. In a block 605, a full signal isapplied to the upper left UL and the lower left LL corners of atouchscreen. In a block 610, a virtual ground is applied to the upperright UR and lower right LR corners of the touchscreen. A predeterminednumber of samples are taken of the four corners of the touchscreen asshown in a block 615 for the sample X. Then, an actual value for the Xsample is determined using the predetermined number of samples as shownin a block 620.

The FIG. 6 shows the embodiment of the invention where an amplituderamped field is generated and ramps from the left hand side to the righthand side across the touchscreen. As will be shown in FIG. 7 below,other aspects of the invention also include various methods that operateto change the direction of the amplitude ramped field across thetouchscreen at various instances in time.

FIG. 7 is a functional block diagram illustrating another embodiment ofa touchscreen processing method 700 that is performed in accordance withcertain aspects of the invention. In a block 705, a full signal isapplied to the upper left UL and the lower left LL corners of atouchscreen. In a block 710, a virtual ground is applied to the upperright UR and lower right LR corners of the touchscreen. A predeterminednumber of samples are taken of the four corners of the touchscreen asshown in a block 715 for the sample X. Then, an actual value for the Xsample is determined using the predetermined number of samples as shownin a block 720.

In a block 725, a full signal is applied to the upper right UR and thelower right LR corners of the touchscreen. In a block 730, a virtualground is applied to the upper left UL and the lower left LL corners ofthe touchscreen. A predetermined number of samples are taken of the fourcorners of the touchscreen as shown in a block 735 for the sample INVX.Then, an actual value for the INVX sample is determined using thepredetermined number of samples as shown in a block 740.

In a block 745, a full signal is applied to the upper left UL and theupper right UR corners of the touchscreen. In a block 750, a virtualground is applied to the lower left LL and the lower right LR corners ofthe touchscreen. A predetermined number of samples are taken of the fourcorners of the touchscreen as shown in a block 755 for the sample Y.Then, an actual value for the Y sample is determined using thepredetermined number of samples as shown in a block 760.

In a block 765, a full signal is applied to the lower left LL and thelower right LR corners of the touchscreen. In a block 770, a virtualground is applied to the upper left UL and the upper right UR corners ofthe touchscreen. A predetermined number of samples are taken of the fourcorners of the touchscreen as shown in a block 775 for the sample INVY.Then, an actual value for the INVY sample is determined using thepredetermined number of samples as shown in a block 780.

The FIG. 7 shows the embodiment of the invention where an amplituderamped field is generated and ramps in four different directions acrossthe touchscreen to generate the measurements X, INVX, Y, and INVY. Allfour of the measurements may be used to discriminate precisely thelocation of a user's touch on the touchscreen. In addition, the order inwhich the measurements of the values X, INVX, Y, and INVY may bere-arranged without departing from the scope and spirit of theinvention.

FIG. 8 is a functional block diagram illustrating another embodiment ofa touchscreen processing method 800 that is performed in accordance withcertain aspects of the invention. In a block 810, all the corners of atouchscreen are simultaneously energized and a Z signal is monitored.This mode of operation enable energy conservation by dissipating nocurrent across the screen; this mode of operation may be used when therehas been a period of time in which there has been no user touch.

In a block 820, the Z measurement may be used to compensate for andmonitor any environmental changes. This may also be used to perform anyoperational changes as well. These changing environmental changes may bestored and the touchscreen system may then modify its operational pointsto accommodate such environmental changes. The drift or changes of theenvironmental changes may be stored in a memory, so that the system isable to adapt, in real time, to the changing environmental conditionsbased on earlier conditions.

Then, in a block 830, it is determined whether a user touch has beendetected. If it is determined that a user touch has occurred in adecision block 840, then one or more amplitude ramped signals may beemployed across the touchscreen as shown in block 850. However, when itis determined that a user touch has not in fact occurred in the decisionblock 840, then the touchscreen processing method 800 returns to theoperations within the block 810.

The Z block data and its processing may be employed for monitoringchanges. One such situation is when no user touch is present on thetouchscreen. There may be several reasons for this. One such reason isthat when Z is being driven, very little current is consumed on thetouchscreen. Another reason is that until Z stabilizes with a touch, theVGA and the integration settings will fluctuate and any X or Y datataken will be unreliable. Yet another reason is that the Z data must beconstantly monitored so that changes in reactance in the circuit andtouchscreen due to temperature, humidity, noise, and changing proximityof bodies in the touchscreen electrostatic field, may be properlyrecorded. There are also alternative manners in which the Z data may beacquired without direct monitoring of it. It may be derived from theother measurements. For example, the Z data may also be obtained bysumming the magnitudes of the X and INVX signals.

FIG. 9 is a diagram illustrating an embodiment of a linear resistivepattern 900 that is arranged around the perimeter of a touchscreen thatis built in accordance with certain aspects of the invention. Asdescribed above, there are a number of various ways in which a linearresistive pattern may be arranged on a touchscreen to effectuate alinear resistive arrangement. The FIG. 9 shows one such embodiment. Theelectrical traces are arranged such that when an amplitude ramped ACsignal is applied to the corners, the field will attenuate linearlyacross the touchscreen. Four different drive signals are provided to thefour corners, shown as ULDRV, LLDRV, URDRV, and LRDRV. The interactionof the FIG. 9 will be described as interacting with the followingFigures as well. It should be noted that the invention could be made towork without a linearization pattern instead using switched discretepoints around the perimeter of the resistive sheet or using anon-linearized pattern with linear correction occurring in the digitalrealm.

FIG. 10 is a circuitry diagram illustrating an embodiment of a cornerdrive circuitry 1000 that is built in accordance with certain aspects ofthe invention. The FIG. 10 shows the use of a digital sine wavegenerator chip with a built in DAC that is operable to supply aprocessor programmable spectrally pure sine wave of fixed amplitude tothe corner driver circuits by way of a digitally controlled amplitudecircuit (see circuitries U8 and U10). The output analog signals areprovided to four comparable gain stages, shown as four operationalamplifiers, from which four different output signals are provided to thefour corner measurement circuits. These four outputs are shown as UR,LR, LL, and UL. Those persons having skill in the art of electricalengineering will appreciate the signal processing shown within theparticular embodiment of the FIG. 10.

FIG. 11 is a circuitry diagram illustrating an embodiment of a cornermeasurement circuitry 1100 that is built in accordance with certainaspects of the invention. For simplicity, only one of the four cornermeasurement circuitries is shown in the FIG. 11. The corner measurementcircuitry 1100 may be replicated and placed at the other three cornersof the linear resistive pattern 900 of the FIG. 9. The output ULDRV,from the FIG. 9, is provided as an input to the corner measurementcircuitry 1100. The UL signal is provided to the corner measurementcircuitry 1100 that services the upper left corner measurement circuitry1100, and the LL signal is provided to a corner measurement circuitrythat services the lower left corner measurement circuitry (not shown).This arrangement is similar with respect to the upper right and lowerright corners of the linear resistive pattern 900 of the FIG. 9 as well.After undergoing the signal processing within the FIG. 11, a resultantsignal UL_I+C is provided as an output from the corner measurementcircuitry 1100. This signal UL_I+C includes the unbalanced capacitivereactance portion of the current measured at the upper left corner ofthe linear resistive pattern 900 of the FIG. 9, namelyI_(XC(unbalanced)). This signal UL_I+C includes the unbalancedcapacitive reactance associated with the touchscreen as well as anyunbalanced capacitive reactance associated with a user's touch on thetouchscreen. Those persons having skill in the art of electricalengineering will appreciate the signal processing shown within theparticular embodiment of the FIG. 11.

FIG. 12 is a circuitry diagram illustrating an embodiment of a high passsingle pole filter/adder circuitry 1200 that is built in accordance withcertain aspects of the invention. The signal UL_I+C from the cornermeasurement circuitry 1100 of the FIG. 11 are provided as inputs to thehigh pass single pole filter/adder circuitry 1200. In addition, thesignals from the corner measurement circuitries are also provided asinputs to the high pass single pole filter/adder circuitry 1200; theother inputs from the other corners are shown as LL_I+C (from the cornermeasurement circuitry of the lower left corner), UR_I+C (from the cornermeasurement circuitry of the upper right corner), and LR_I+C (from thecorner measurement circuitry of the lower right corner). The signalsumming functionality of the high pass single pole filter/addercircuitry 1200, within the FIG. 12, will be appreciated by those personshaving skill in the art of electrical engineering. The interaction ofthe FIG. 12 will be also described as interacting with the followingFigures as well. The individual corner signals are passed through a highpass single pole filter and added together. High pass filtering occursdue to AC coupling between stages with a lower cutoff frequency around15 kHz. Adding the outputs of the HIGH SIDE and LOW SIDE driver circuitseffectively removes the current portion of the signal due solely to theresistance across the touchscreen, leaving only the unbalanced reactiveportion of the current as a voltage signal.

FIG. 13 is a circuitry diagram illustrating an embodiment of a low passdouble pole filter/gain stage circuitry 1300 that is built in accordancewith certain aspects of the invention. At this point a single signalcontaining only the unbalanced reactive current is amplified X10 and fedinto a double pole low pass filter. The low pass filter at this stage,with an upper cutoff in a particular frequency range (e.g., the 200 kHzrange in some embodiments), reduces any high frequency components andharmonics. The output signal from the high pass single pole filter/addercircuitry 1200 is provided as the input to the low pass double polefilter/gain stage circuitry 1300.

FIG. 14 is a circuitry diagram illustrating an embodiment of a nullsignal generation circuitry 1400 that is built in accordance withcertain aspects of the invention. A digital sine wave generator chipwith a built in DAC will supply a processor programmable spectrally puresine wave of varying amplitude and phase as an output from the FIG. 14.The null signal, shown as NULL_SIG, is provided as an output from thenull signal generation circuitry 1400 of the FIG. 14. Those personshaving skill in the art of electrical engineering will appreciate thesignal processing shown within the particular embodiment of the FIG. 14.

FIG. 15 is a circuitry diagram illustrating an embodiment of a nullsignal adding circuitry that 1500 is built in accordance with certainaspects of the invention. The output signal from the FIG. 14, namely thenull signal NULL_SIG, is provided to the to the null signal addingcircuitry that 1500 of the FIG. 15. In addition, the other input to thenull signal adding circuitry that 1500 is the output of the low passdouble pole filter/gain stage circuitry 1300 of the FIG. 13.

The cooperative operation within the FIGS. 14 and 15 may be described asfollows: the unbalanced reactive load on the touchscreen will take theform of a sine wave with a phase shift from the primary touchscreendrive signal. The amplitude and phase of the signal will be theintegration of all the unbalanced capacitive reactance in the circuit.This includes the background grounding capacitive reactance of thescreen and any touch reactance. Measuring this signal without a touchand removing it (nulling) leaves only the users touch current, left inthe form of amplitude changes to the signal. Then, by generating a sinewave with a −180 deg phase and of similar amplitude and by adding thissignal to the touchscreen signal, it can be almost completely zeroed.The remaining signal will contain some unbalanced capacitive reactance.Any changes to this signal will be due to one or more of noise inducedinto the touchscreen or circuit, temperature variations to the circuitsor touchscreen, and humidity variations to the circuit or touchscreen.

FIG. 16 is a circuitry diagram illustrating an embodiment of a DSPcircuitry 1600 that is built in accordance with certain aspects of theinvention. The output of the null signal adding circuitry that 1500 ofthe FIG. 15, after having passed through another low pass double polefilter/gain stage circuitry (which may be a replication of the same lowpass double pole filter/gain stage circuitry 1300 of the FIG. 13) isprovided to the DSP circuitry 1600 as the signal AUX1 (on the analog todigital converter chip depicted herein). The DSP circuitry 1600 performsthe functionality described above in the various embodiments to discernthe particular location of a user's touch on the touchscreen. Thosepersons having skill in the art of electrical engineering willappreciate the signal processing shown within the particular embodimentof the FIG. 16.

FIG. 17 is a functional block diagram illustrating an embodiment offunctional cooperation performed by the various circuitries shown withinthe FIGS. 9, 10, 11, 12, 13, 14, 15, and 16. The signal ULDRV isprovided from the touchscreen corner of the FIG. 9. This ULDRV signal isprovided to the corner measurement circuitry 1100 of the FIG. 11. Inaddition, the corner drive circuitry 1000 of the FIG. 10 provides thesignal UL to the corner measurement circuitry 1100 of the FIG. 11 fromwhich the signal UL_I+C is output and passed to the high pass singlepole filter/adder circuitry 1200 of the FIG. 12. It is noted thatsignals LLDRV, URDRV, and LRDRV are provided from the other cornermeasurement circuitries associated with the three corners as well, andthey generate the signals LL_I+C, UR_I+C, and LR_I+C that are allprovided to the high pass single pole filter/adder circuitry 1200 alongwith the signal UL_I+C. The output of the high pass single polefilter/adder circuitry 1200 of the FIG. 12 is provided to the low passdouble pole filter/gain stage circuitry 1300. The output of the low passdouble pole filter/gain stage circuitry 1300 is provided to the nullsignal adding circuitry that 1500, where the output from the null signalgeneration circuitry 1400 is added in. The output of the null signaladding circuitry that 1500 is provided to another low pass double polefilter/gain stage circuitry 1305; this low pass double pole filter/gainstage circuitry 1305 may be a replica of the low pass double polefilter/gain stage circuitry 1300 of the FIG. 13. The output of the lowpass double pole filter/gain stage circuitry 1305 is provided to the DSPcircuitry 1600 of the FIG. 16.

It is also noted that the various circuitries presented herein may alsobe compacted or integrated into fewer (or more) circuitry componentswithout departing from the scope and spirit of the invention. Forexample, the functionality presented herein may be implemented usingmore or less blocks and/or circuitry to perform similar or analogousfunctionality without departing from the scope and spirit of theinvention.

In view of the above detailed description of the invention andassociated drawings, other modifications and variations will now becomeapparent to those skilled in the art. It should also be apparent thatsuch other modifications and variations may be effected withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A touchscreen system, comprising: a dielectricsheet having a frontside and a backside; a resistive pattern that isattached to the backside of the dielectric sheet; a plurality of drivesignal circuits that are respectively coupled to a correspondingplurality of communicative coupling points of the resistive pattern onthe backside of the dielectric sheet to produce a first pair of twoamplitude ramped fields having inversed gradients with respect to eachother in a first direction by applying full scale AC signals to a firstset of the plurality of communicative coupling points and virtual groundsignals to a second set of the plurality of coupling points at a firsttime and applying the virtual ground signals to the first set of theplurality of communicative coupling points and the full scale AC signalsto the second set of the plurality of coupling points at a second time,each of the amplitude ramped fields communicatively coupling through thedielectric sheet to the frontside of the dielectric sheet, the pluralityof drive signal circuits being further operable to measure current flowat the plurality of communicative coupling points coupled to theresistive pattern on the backside of the dielectric sheet, the firstpair of amplitude ramped fields including: a first amplitude rampedfield extending across the dielectric sheet in the first direction atthe first time, and a second amplitude ramped field extending across thedielectric sheet in the first direction at the second time subsequent tothe first time; and a digital signal processor that is operable to:extract a first unbalanced capacitive component of the measured currentflow at the plurality of communicative coupling points at the first timeand a second unbalanced capacitive component of the measured currentflow at the second time; and derive a location in the first direction ofthe user's interaction or touch on the frontside of the dielectric sheetby deriving a ratio of the first unbalanced capacitive component to asum of the first unbalanced capacitive component and the secondunbalanced capacitive component.
 2. The touchscreen system of claim 1,wherein the touchscreen system: sums currents corresponding to the firstand second amplitude ramped fields.
 3. The touchscreen system of claim1, further comprising: nulling and adding circuitry that is operable toreduce a non-user touched portion of the unbalanced capacitive reactancecurrent portion and to increase an overall resolution of the unbalancedcapacitive reactance current portion that is substantially attributableto the user's interaction or touch on the touchscreen.
 4. Thetouchscreen system of claim 1, wherein: the dielectric sheet furtherincludes four corners; the plurality of drive signal circuits includesfour drive signal circuits; the four drive signal circuitssimultaneously energize all four corners of the dielectric sheet with afull scale AC signal when the digital signal processor fails to detect auser's interaction or touch on the frontside of the dielectric sheet fora predetermined period of time; the digital signal processor detects andcompensates for at least one of a temperature variation of thetouchscreen system and a humidity variation of the touchscreen system;the touchscreen system operates in an energy conservation mode; and thedigital signal processor exits the energy conservation mode afterdetecting the user's interaction or touch on the frontside of thedielectric sheet.
 5. The touchscreen system of claim 4, wherein: thefour drive signal circuits energize the resistive pattern therebygenerating the first amplitude ramped field that extends across thesurface of the dielectric sheet in the first direction when the digitalsignal processor detects the user's interaction or touch on thefrontside of the dielectric sheet.
 6. The touchscreen system of claim 1,further comprising: a plurality of subtraction circuits, each of theplurality of subtraction circuits being communicatively coupled to oneof the plurality of drive signal circuits operable to produce aresulting current flow having the first unbalanced capacitive componentat the first time and the second unbalanced capacitive component at thesecond time.
 7. The touchscreen system of claim 6, wherein the pluralityof subtraction circuits are operable to remove any substantially purelyresistive current portion that is injected into one of the correspondingplurality of communicative coupling points by one of the plurality ofdrive signal circuits.
 8. The touchscreen system of claim 1, wherein theplurality of drive signal circuits further produce a second pair ofamplitude ramped fields having inversed gradients with respect to eachother in a second direction perpendicular to the first direction, thesecond pair of amplitude ramped fields including: a third amplituderamped field extending across the dielectric sheet in the seconddirection at a third time subsequent to the second time by applying fullscale AC signals to a first set of the plurality of communicativecoupling points and virtual ground signals to a second set of theplurality of communicative coupling points, and a fourth amplituderamped field extending across the dielectric sheet in the seconddirection at a fourth time subsequent to the third time by applying thevirtual ground signals to the third set of the plurality ofcommunicative coupling points and the full scale AC signals to thefourth set of the plurality of communicative coupling points, the fourthamplitude ramped field having an inversed gradient with respect to thethird amplitude ramped field; wherein the digital signal processorderives a second ratio of the third unbalanced capacitive component to asum of the third unbalanced capacitive component and the fourthunbalanced capacitive component to produce a second position of thelocation in the second direction.
 9. A touchscreen system, comprising: adielectric sheet having a frontside and a backside; a resistive patternthat is attached to the backside of the dielectric sheet; a plurality ofdrive signal circuits that are communicatively coupled to the resistivepattern on the backside of the dielectric sheet at respective ones of aplurality of communicative coupling points, wherein each of theplurality of drive signal circuits is respectively operable to measurecurrent flow at a respective one of the plurality of communicativecoupling points coupled to the resistive pattern on the backside of thedielectric sheet; wherein the plurality of drive signal circuits arecooperatively operable to energize the resistive pattern therebygenerating a plurality of amplitude ramped fields that eachcommunicatively couple through the dielectric sheet to the frontside ofthe dielectric sheet, the plurality of amplitude ramped fieldsincluding: a first amplitude ramped field extending across thedielectric sheet in a first direction at a first time by applying fullscale AC signals to a first set of the plurality of communicativecoupling points and virtual ground signals to a second set of theplurality of communicative coupling points, a second amplitude rampedfield extending across the dielectric sheet in the first direction at asecond time subsequent to the first time by applying the virtual groundsignals to the first set of the plurality of communicative couplingpoints and the full scale AC signals to the second set of the pluralityof communicative coupling points, the second amplitude ramped fieldhaving an inversed gradient with respect to the first amplitude rampedfield, a third amplitude ramped field extending across the dielectricsheet in a second direction perpendicular to the first direction a thirdtime subsequent to the second time by applying the full scale AC signalsto a third set of the plurality of communicative coupling points and thevirtual ground signals to a fourth set of the plurality of communicativecoupling points, and a fourth amplitude ramped field extending acrossthe dielectric sheet in the second direction at a fourth time subsequentto the third time by applying the virtual ground signals to the thirdset of the plurality of communicative coupling points and the full scaleAC signals to the fourth set of the plurality of communicative couplingpoints, the fourth amplitude ramped field having an inversed gradientwith respect to the third amplitude ramped field; subtraction circuitryoperable to remove any substantially purely resistive current portionthat is injected by one of the drive signal circuits, the subtractioncircuitry also operable to remove current not having an unbalancedcapacitive component that is substantially attributable to a user'sinteraction or touch on the frontside of the dielectric sheet; and adigital signal processor that is operable to: extract a first unbalancedcapacitive component of the measured current flow at the first time, asecond unbalanced capacitive component of the measured current flow atthe second time, a third unbalanced capacitive component of the measuredcurrent flow at the third time and a fourth unbalanced capacitivecomponent of the measured current flow at the fourth time; and derive alocation of the user's interaction or touch on the frontside of thedielectric sheet by deriving: a first ratio of the first unbalancedcapacitive component to a sum of the first unbalanced capacitivecomponent and the second unbalanced capacitive component to produce, afirst position of the location in the first direction; and a secondratio of the third unbalanced capacitive component to a sum of the thirdunbalanced capacitive component and the fourth unbalanced capacitivecomponent to produce a second position of the location in the seconddirection.
 10. The touchscreen system of claim 9, wherein: thedielectric sheet further includes four corners; the plurality of drivesignal circuits includes four drive signal circuits; the four drivesignal circuits are respectively coupled to the resistive pattern at thefour corners of the dielectric sheet; and each of the four drive signalcircuits is operable to measure current flow at an associated corner ofthe dielectric sheet and to detect a respective one of the first,second, third and fourth unbalanced capacitive components of themeasured current attributable to the user's interaction or touch on thefrontside of the dielectric sheet.
 11. The touchscreen system of claim10, further comprising: four subtraction circuits, each subtractioncircuit being respectively communicatively coupled to one of the fourdrive signal circuits and each subtraction circuit being respectivelyoperable to subtract current not attributable to the user's interactionor touch on the frontside of the dielectric sheet.
 12. The touchscreensystem of claim 9, further comprising: nulling and adding circuitry thatis operable to reduce a non-user touch portion of the unbalancedcapacitive reactance current portion and to increase an overallresolution of the unbalanced capacitive reactance current portion thatis substantially attributable to the user's interaction or touch on thetouchscreen.
 13. A method for operating a touchscreen system, the methodcomprising: cooperatively energizing a resistive pattern attached to abackside of a dielectric sheet at a plurality of communicative couplingpoints and generating a plurality of amplitude ramped fields that eachcommunicatively couple through the dielectric sheet to a frontside ofthe dielectric sheet, the cooperatively energizing the resistive patternincluding: applying full scale AC signals to a first set of theplurality of communicative coupling points and virtual ground signals toa second set of the plurality of communicative coupling points toproduce a first amplitude ramped field extending across the dielectricsheet in a first direction at a first time, applying the virtual groundsignals to the first set of the plurality of communicative couplingpoints and the full scale AC signals to the second set of the pluralityof communicative coupling points to produce a second amplitude rampedfield extending across the dielectric sheet in the first direction at asecond time subsequent to the first time, the second amplitude rampedfield having an inversed gradient with respect to the first amplituderamped field, applying the full scale AC signals to a third set of theplurality of communicative coupling points and the virtual groundsignals to a fourth set of the plurality of communicative couplingpoints to produce a third amplitude ramped field extending across thedielectric sheet in a second direction perpendicular to the firstdirection a third time subsequent to the second time, and applying thevirtual ground signals to the third set of the plurality ofcommunicative coupling points and the full scale AC signals to thefourth set of the plurality of communicative coupling points to producea fourth amplitude ramped field extending across the dielectric sheet inthe second direction at a fourth time subsequent to the third time, thefourth amplitude ramped field having an inversed gradient with respectto the third amplitude ramped field; measuring current flow at theplurality of communicative coupling points coupled to the resistivepattern on the backside of the dielectric sheet at each of the first,second, third and fourth times; removing any substantially purelyresistive current portion that is injected at the plurality ofcommunicative coupling points and removing current not having anunbalanced capacitive component thereby generating a first unbalancedcapacitive component at the first time, a second unbalanced capacitivecomponent at the second time, a third unbalanced capacitive component atthe third time and a fourth unbalanced capacitive component at thefourth time; converting the first, second, third and fourth unbalancedcapacitive component, being substantially attributable to a user'sinteraction or touch on the frontside of the dielectric sheet, to first,second, third and fourth digital signals, respectively; deriving, in adigital signal processor, a location of the user's interaction or touchon the frontside of the dielectric sheet deriving including: deriving afirst ratio of the first digital signal to a sum of the first digitalsignal and the second digital signal to produce a first position of thelocation in the first direction, and deriving a second ratio of thethird digital signal to a sum of the third digital signal and the fourthdigital signal to produce a second position of the location in thesecond direction.
 14. The method of claim 13, further comprising:reducing a non-user touch portion of the unbalanced capacitive reactancecurrent portion; and increasing an overall resolution of the unbalancedcapacitive reactance current portion that is substantially attributableto the user's interaction or touch on the touchscreen.
 15. The method ofclaim 13, wherein: the dielectric sheet includes four corners; andfurther comprising: simultaneously energizing all four corners of thedielectric sheet with a full scale AC signal when the digital signalprocessor fails to detect a user's interaction or touch on the frontsideof the dielectric sheet for a specified period of time; compensating forat least one of a temperature variation of the touchscreen system and ahumidity variation of the touchscreen system; operating in an energyconservation mode; and exiting the energy conservation mode afterdetecting the user's interaction or touch on the frontside of thedielectric sheet.
 16. The method of claim 13, further comprising:energizing the resistive pattern and generating the first amplituderamped field that extends across the surface of the dielectric sheet inthe first direction when the digital signal processor detects the user'sinteraction or touch on the frontside of the dielectric sheet.
 17. Atouchscreen system, comprising: a touchscreen having a frontside and abackside; a resistive pattern that is attached to the backside of thetouchscreen; a plurality of drive signal circuits that arecommunicatively coupled to the resistive pattern at communicativecoupling points, each drive signal circuit within the plurality of drivesignal circuits is also operable to measure current flow at thecommunicative coupling points of each drive signal circuit within theplurality of drive signal circuits to the touchscreen; wherein eachdrive signal circuit within the plurality of drive signal circuitsoperates cooperatively to energize the resistive pattern therebygenerating an amplitude ramped field that communicatively couplesthrough the touchscreen to the frontside of the touchscreen and extendsacross the frontside of the touchscreen in a direction, the directionbeing selectable by applying full scale AC signals to some of thecommunicative coupling points and virtual ground signals to othercommunicative coupling points, the amplitude ramped field is operable tobe selectively ramped in a plurality of directions across thetouchscreen; a plurality of subtraction circuits, each subtractioncircuit being communicatively coupled to one of the plurality drivesignal circuits and each subtraction circuit being operable to removeany substantially purely resistive current portion that is injected intoone of the corners by one of the drive signal circuits, each of thesubtraction circuits also being operable to perform high pass filteringand adding to remove any resistance portion of the current flow at thecorners of the touchscreen thereby leaving a resulting current flowhaving an unbalanced capacitive reactance current portion; an analog todigital converter that converts the unbalanced capacitive reactancecurrent portion that is substantially attributable to a user's touch onthe touchscreen to a digital signal; wherein the current flow at thepoints of communicative coupling includes an unbalanced capacitivereactance current portion wherein a change of the unbalanced capacitivereactance current portion includes a portion that is substantiallyattributable to a user's interaction or touch on the touchscreen; and adigital signal processor that is operable to process a digital versionof the change of the unbalanced capacitive reactance current portion todiscriminate a location of the user's interaction or touch on thetouchscreen.